Take a look at TP-Link's range of routers. They seem to be the best bang for the buck. They will run DD-WRT, not sure about Tomato. I have never seen a bad review and they have a model in your price range.
Asus will run DD-WRT or Tomato. I have an RT-N16 running Tomato and it kicks ass. However as you fear, probably outside your price range.